The maximum a-posteriori probability (MAP) algorithm is used in a number of coding schemes to improve the performance of communication systems. Maximum a-posteriori probability (MAP) decoders are used in, for example, turbo code-based radio frequency (RF) transceivers. Turbo coding is a powerful forward error correction (FEC) algorithm that achieves a coding gain close to the Shannon limit. Turbo encoders and turbo decoders have been adopted for use in the physical layers of a number of wireless standards, including WCDMA, CDMA2000, IEEE-802.16e (i.e., WiBro) and others. Thus, MAP decoders are implemented in, for example, WCDMA 8PCCC turbo decoders and in 802.16/Wibro CTC turbo decoders.
A software-defined radio (SDR) device uses reconfigurable hardware that may be programmed over-the-air to operate under different wireless standards. For example, an SDR transceiver in a wireless laptop computer or PDA may be configured by different software loads to operate in an IEEE-802.11x wireless network, a CDMA2000 wireless network, an OFDM/OFDMA wireless network, a GSM wireless network, or other types of networks. Many of these wireless standards require the use of turbo decoders or other decoders that are based on maximum a-posteriori probability (MAP) decoders.
However, conventional decoders have significant drawbacks with respect to SDR applications. Turbo decoders and other types of decoders are optimized for decoding under only one or two specific standards. Conventional designs use different MAP decoders to support each standard separately. For example, a MAP decoder calculates three values: alpha (α), beta (β), and lambda (λ). Normally, three distinct hardware blocks are used to calculate these values. This increases power consumption and uses a large amount of die space.
If an SDR device is required to support many wireless standards, more than one decoder must be implemented in the SDR device. This leads to a complex transceiver design that makes inefficient use of chip space and has high power dissipation. This also increases development cost and time-to-market (TTM). Additionally, some of the newer wireless standards operate at relatively high data rates (e.g., WiBro, HSPDA, and the like). A decoder that is optimized in terms of speed and power consumption for a low data rate standard is unlikely to be optimized in terms of speed and power consumption for a high data rate standard, and vice versa. Thus, conventional decoder designs are not suitable for use in SDR applications.
Therefore, there is a need in the art for an improved reconfigurable decoder for use in a software-defined radio (SDR) system. In particular, there is a need for a maximum a-posteriori probability (MAP) decoder that may be implemented in a reconfigurable decoder that operates under different wireless standards.